This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-105948, filed Apr. 4, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a position control device of a power zoom lens of a camera.
2. Description of the Related Art
Generally, to realize a reduction in size and weight of a camera, sharing or simplifying a driving mechanism and a driving-source is being improved. The driving source is used for various applications such as film transport, driving (zooming and focusing) of a photographic lens, and the like through a switching mechanism mounting a single motor. As the above-mentioned driving mechanism, for example, a step zoom mechanism is known. In the step zoom mechanism, zooming is performed stepwise by a single motor, focal length is varied on the basis of the zooming, and after that, the operation is switched to focal point adjustment (focusing).
As the step zoom mechanism, for example, there is a mechanism disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-313834. A camera according thereto has a first propeller coupled to a shaft of a motor and a second propeller coupled to a shaft provided for one gear included in a gear train. When the motor is driven, the propellers are rotated in photo-interrupters disposed for the propellers, thereby generating pulse signals. On the basis of the pulse signals, a zoom lens barrel is driven and the focusing operation is controlled.
The step zoom mechanism uses a zoom lens frame in which zooming regions, where the focal length is changed, and focusing regions, where the focal point is adjusted, are alternately arranged stepwise. Accordingly, when the zoom lens frame cannot be stopped at a proper position in the zooming region at the lens driving time, there is a problem in that the accuracy of focusing performed thereafter is degraded.
Even when the zoom lens frame is stopped at the proper position at zoom stop time, the position of the lens frame may be shifted due to the application of an external force or the like. Similarly in this case, there is a problem in that the accuracy of focusing performed thereafter is degraded.
In Jpn. Pat. Appln. KOKAI Publication No. 6-313834 mentioned above, the signal generated by the rotation of the propeller provided for the middle portion of the gear train for driving the lens frame is used for control at the lens driving time. Accordingly, it is difficult to perform the correct position control due to an influence of backlash in the gear train. In this constitution, when an external force is applied to shift the position of the lens frame, focusing may be performed in the zooming region. Consequently, it is difficult to accurately perform the focusing control.
A first object of the present invention is to provide a zoom lens position control device, wherein a position of a step zoom with high accuracy is detected with a simple constitution to correctly perform focal length shift and focal point adjustment. A second object of the present invention is to provide a zoom lens position control device, wherein when an external force is applied and the stopping position of a zoom lens is shifted, the operation can be subsequently switched to exposure from a correct focal length position, and focusing control with high accuracy can be performed with a simple constitution.
To accomplish the above objects, according to the invention, there is provided a zoom lens position control device including: a zoom lens having a plurality of zoom steps in which a plurality of steps each including a focal length changing region and a focal point adjusting region are continuously arranged; driving means for driving the zoom lens; switching means in which the ON/OFF state is changed due to a shift between the focal length changing region and the focal point adjusting region; detecting means for detecting the ON/OFF state of the switching means; and control means for stopping driving the zoom lens in accordance with the detection of a change in the state of the switching means through the detecting means. The zoom lens position control device further includes a memory which stores a position where the zoom lens is stopped. When the zoom lens is moved from the stopping position stored in the memory, the zoom lens is shifted to an initial position.
According to the present invention, there is provided a camera including: a step zoom driving mechanism in which regions, where a focal length is changed, and regions, where focal point adjustment is performed, are alternately arranged stepwise, and which moves a photographic lens so that the photographic lens is located in the regions by turns, the step zoom driving mechanism including (a) a movable lens frame, (b) a motor which drives the movable lens frame, and an encoder which detects a displacement state of the movable lens frame, the encoder generating different kinds of signals in the focal length changing region and the focal point adjusting region; and a controller which controls the motor on the basis of the output signal of the encoder to instruct the focal length changing operation and the focal point adjustment operation.
According to the zoom lens position control device with the constitution as mentioned above, when the stopping position of the zoom lens is shifted due to the application of an external force, the detecting means detects a change in the state of the switching means to initialize the stopping position of the zoom lens.